Engine-powered generators are commonly used as standby AC power generation equipment for residences and businesses in order to provide power when utility power fails. Transfer switches are commonly used as the means of connecting the generator to the building AC wiring.
Two types of transfer switches are available, manual and automatic.
Manual transfer switches rely on a human operator to operate the switch. When power fails, the operator must start the generator and then throw switches on the manual transfer switch to transfer selected loads from utility power to generator power. When utility power is restored, the operator reverses this process, shutting down the generator and throwing switches on the transfer switch to reconnect the loads to utility power. Manual transfer switches are inexpensive, but require a human operator to be present. Emergency situations commonly occur when a human operator is not present.
Automatic transfer switches have internal logic which can detect utility power failure, signal a generator to start, and then transfer the load from the utility to the generator, reversing this process when the utility power is restored.
Automatic transfer switches (ATS) currently available provide a RUN signal to an external engine controller. The engine controller has the responsibility to start and stop the generator (based on the RUN signal from the ATS). Some engine controllers also provide extra inputs for alarm signals from the generator such as low oil pressure and high temperature. The engine controller may take some action based on these inputs, but there is no communication of what has occurred back to the ATS. Any visual indications of a problem are only available at the engine controller, which is mounted in the vicinity of the generator, normally outside the building.
Engine controllers typically include only a low current relay output for the engine starter that can only handle a few amps, so an external contactor must be obtained and connected to the engine starter and battery to provide the capability of switching the 100 amps or so required by the engine starter motor.
Engine controllers normally provide a relay contact to operate the engine choke. This is fine for engines having an electrically-operated choke. Unfortunately most small portable (less than 13,000 watts) generators have mechanically-operated chokes.
ATS units are typically available in sizes from 100 amps on up. Residences and small businesses typically need a generator in the range of 50 amps maximum, so ATS units having larger maximum capabilities are not necessary for these uses and incorporate larger associated costs.
Engine controllers may include a battery charger function, but the battery status is not communicated back to the ATS, and if any visual indication of battery status is available, it is only available at the engine controller location (normally outside the building).
The present invention aims to solve the problems mentioned above that exist with currently available ATS and engine controllers.
At the heart of the ATS is a pair of double-pole switch/circuit breakers (switches) operated by a servo motor. The switching elements can be either a simple switch or a combined switch/circuit breaker. The addition of the circuit breaker function provides additional protection for both the generator and its wiring as well as for the loads connected to the switch. One side of each double-pole switch is connected to an electrical supply source, such as a utility or a generator. The other side of each switch is connected in common to a load subpanel or manual transfer switch. The load subpanel or manual transfer switch is in turn connected to selected loads.
An actuator mounted on the servo motor serves both to operate the switches and to function as an interlock to prevent both switches from being on simultaneously, thus causing a line-to-line short circuit. The stacked combination of the switches forms the function of a double pole double throw switch. The servo motor operator can then be electrically activated to move the operating handles to one side or the other, thus turning one double pole switch/breaker OFF while simultaneously turning the other double pole switch/breaker ON. The actuator works in such a way that the switch going to the OFF position opens before the other switch goes ON, thus ensuring a xe2x80x9cbreak-before-makexe2x80x9d operation, preventing any short-circuiting of the utility and generator voltages. The servo motor mechanism allows the switch to be operated manually without damaging the servo motor, while the actuator prevents both switches from being on simultaneously even when operated manually.
The ATS also includes a logic section to control its operation and to communicate with the engine controller. The logic section controls the servo motor, detects the presence or absence of AC voltage from the utility, from the generator, and to the load. It also detects the physical position of the two double pole switch/breakers via auxiliary switches mechanically tied to the switch/breaker operators, since manual operation or tripping of the circuit breaker function may move the switch to a different status than is thought to be true by the logic section or a welded switch contact may prevent the switch from being turned off. The logic section is setup to monitor its various inputs and then take appropriate action based on the state of these inputs.
A power supply is included in the ATS. The power supply provides power to the logic section, engine controller, and also for a battery charger function included as part of the engine controller.
The ATS incorporates bi-directional communication with the engine controller. This allows not only sending a RUN signal to the engine controller as is done with currently available ATS units, but also sending and receiving other information between the ATS and engine controller. Such things as battery status can be communicated, allowing the ATS to visually display battery status at the ATS location. The ATS can also tell the engine controller when the ATS detects AC voltage on the generator output. The engine controller can then stop cranking the engine starter. The ATS and engine controller can also detect when the communication link is broken, and provide a visual indication to the operator of this fact.
Since the ATS function is servo motor operated, the motor can be stopped at any position of its travel. This allows pausing the switch movement at a point when the switch supplying the load opens. The logic section can then monitor presence of voltage on the load, and resume servo motor operation to move the switch to the opposite position when voltage below a set threshold is no longer detected. This prevents switching a load such as a still-spinning motor to a supply where the motor""s self-generated voltage may be out of phase with the utility or generator-supplied voltage, resulting in a large, possibly damaging current surge. Also, when the servo motor moves the switches through the position where both are OFF, the logic section can monitor the auxiliary switches to be sure that the switch/circuit breaker that was ON truly goes off. If the auxiliary switch would still indicate that the OFF switch was on, the logic section would stop further movement of the servo motor to prevent a line-to-line short.
Since the servo motor is not damaged by manual operation of its shaft, the ATS may be manually operated. This provides a measure of operational redundancy in that if the automatic operation of the ATS or engine controller fails, the operator can still start the generator manually and switch the load to the generator manually.
At the heart of the engine controller is a microcontroller-based logic section. This logic section communicates with the logic section of the ATS. The engine controller includes electrical relay outputs to control the engine ignition, electrically-operated choke, fuel/gas valve and glow plug relay. A starter contactor provides for direct control of the engine starter motor without the need for an external contactor.
The engine controller includes a mechanical actuator for a mechanical choke. This actuator includes a mechanical linkage allowing easy connection to most small generator choke operators.
The engine controller also includes a battery charger function. Battery terminal voltage and ambient temperature are detected, and charging current and voltage are adjusted accordingly in order to match the charging specifications of the battery. Battery status is reported back to the ATS. Battery charging is inhibited if the battery is fully charged or has a terminal voltage below a set threshold.